Multiple transmission lines have the icing hidden fault when a large area of ice disaster happens to power grid, and the stable operation of power system will be seriously threatened. Therefore, the ice-melting scheme should be developed in advance to arrange the order of ice-melting reasonably. In order to analyze the outage risk of power grid caused by the continuous operation of icing-hidden transmission lines, it's needed to expand the substation main electrical wiring, which is associated with the transmission line needing to melt ice. An improved cutting load model is proposed to assess power grid outage risk of the combination network of transmission grid and substation. And a breaker reliability model is set up to access the outage risk caused by the continuous operation of transmission lines which queue at the rear of ice-melting queue. Icing rate is calculated based on line icing growth model considering wind speed and rainfall, and the ice melting lines set is determined by the icing rate threshold. Power system global icing index is proposed based on icing severity model. Considering the outage risk of power system and global icing index, the ice melting urgent degree index is proposed to dynamically update the ice melting lines set, and determine the ice melting order. Finally, the feasibility and rationality of the proposed method is verified by taking IEEE RBTS as an example.